Actuation systems

ABSTRACT

An actuation system for a vehicle in which a pump (10b) draws fluid from a reservoir (10a) to supply one or more first consumers, such as steering valve (50). One of more second consumers, such as a clutch actuator (12), are actuated via a solenoid valve (12a) from an accumulator (10c) charged by the pump. The solenoid valve connects each second actuator (12) to the accumulator or to the reservoir. When the pressure in the accumulator is below a predetermined charge pressure, flow to the first consumer is restricted to a level sufficient to ensure effective operation of the first consumer, while generating a back pressure sufficient to ensure charging of the accumulator. The flow restriction to the first consumer may be achieved by the solenoid valve (12a) or by a separate charging valve (20).

This invention relates to fluid pressure operated actuation systems andin particular, though not exclusively, to such actuation systems for theoperation of vehicle clutches used in semi-automatic transmissions ofthe form described in, for example, the Applicants earlier Europeanpatents Nos. 0038113, 0043660, 0059035 and 0101220 and other fluidpressure operated functions.

Actuation systems are already known in which a pump supplies pressurisedfluid to interconnected closed centre and open centre circuits each ofwhich includes at least one consumer and the closed centre circuitsincludes an accumulator which is charged by the pump.

Problems arise with such actuating systems in that the operation of theopen centre circuit is often affected by the charging of the accumulatorin the closed centre circuit.

It is an object of the present invention to provide an actuating systemwhich at least mitigates the above problem.

Thus according to the present invention there is provided an actuationsystem comprising:

a pump which draws fluid from a reservoir;

one or more first consumers actuated from the pump;

one or more second consumers actuated via valve means from anaccumulator charged by the pump;

the valve means being operable to connect the or each second consumer tothe accumulator or to the reservoir thus actuating the second consumersand also being operable in response to accumulator pressure levels belowa predetermined charge level to restrict the flow of fluid to the oreach first consumer to a level sufficient to ensure effective operationof the or each first consumer whilst generating a back pressuresufficient to ensure charging of the accumulator.

By restricting the flow to the first consumer(s) when charging of theaccumulator is required in the above manner unaffected operation of thefirst consumer(s) is ensured.

Both the first and second consumers may be actuated via the valve means.

The valve means may include a first valve having a valve member (such asa spool) which is displaceable both to connect the second consumer(s) tothe accumulator or reservoir and also to restrict the flow of fluid tothe first consumer(s).

The valve member may be displaced by a solenoid which is activated by acontrol means which controls operation of the second consumer(s) andalso by signals from an accumulator pressure level sensor. Alternativelythe displacement of the valve member in response to the accumulatorpressure level falling below the predetermined charge level could beachieved by the action of fluid pressure on the valve member.

Where a spool type valve member is used in the first valve means thespool may be provided with one or more grooves or other formationthrough which the restricted flow to the first consumer(s) takes place.

In an alternative construction the valve means may include a first valvehaving a valve member which is displaced both to connect the secondconsumer(s) to the accumulator or reservoir and also to control the rateof charging of the accumulator.

The actuation system may include a separate charging valve means torestrict the flow of fluid to the or each first consumer at accumulatorpressure levels below a predetermined charge level.

The actuation system may also include a second valve means to limit thepressure level to which the accumulator can be charged. Convenientlythis second valve means may comprise a charging valve and venting valvearrangement of the form 94 20983.0 the disclosure of which is herebyincluded in the present application.

Several embodiments of the present invention will now be described, byway of example with reference to the accompanying drawing in which:

FIG. 1 shows details of a clutch/steering actuation system in accordancewith the present invention;

FIG. 2 shows details of a charging and venting valve arrangement whichmay be used in the system of FIG. 1;

FIG. 3 shows details of a second form of clutch/steering actuationsystem in accordance with the present invention;

FIG. 4 shows details of a further form of clutch/steering actuationsystem in accordance with the present invention which employs a chargingand venting valve arrangement similar to that shown in FIG. 2, and

FIG. 5 shows an alternative form of part of the system shown in FIG. 4.

Referring to FIG. 1, the clutch actuation system includes a powerpack 10which supplies pressurised fluid to a first consumer in the form of anopen centre power steering valve 50 and a second consumer in the form ofan actuator 12 for a and a second consumer in the form of an actuator 12for a clutch operating slave cylinder 11. Both consumers are suppliedvia a value means in the form of a solenoid operated fluid flow controlvalve 12a. The slave cylinder 11 acts on a clutch actuating lever 13which in turn operates a clutch release bearing 14.

The powerpack 10 includes a reservoir 10a, an electrically driven pump10b, an accumulator 10c and a non return valve 10d.

Actuator 12 includes a piston 17 which divides the actuator into twochambers 18 and 19 which are connected with solenoid valve 12a and slavecylinder 11 respectively. Thus pressurisation of chamber 18 displacespiston 17 which expels fluid out of chamber 19 to operate slave cylinder11 and displace clutch operating lever 13 to disengage the associatedclutch.

Displacement of clutch operating lever 13 is measured by a sensor in theform of a rotary potentiometer 44 whose output is fed to an electricalcontrol unit 36. Control unit 36 also receives other vehicle operatingparameter inputs, designated S in FIG. 1, and issues commands to thesolenoid 12b of valve 12a to connect the actuator 12 to accumulator 10cor reservoir 10a.

Full constructional and operational details of the electronic controlunit 36 etc. can be found in the Applicants previously referred toEuropean patent nos. and will not therefore be given here.

Solenoid operated valve 12a comprises an outer portion 30 which isinserted into a bore 31 in a housing 15 and remains stationary therein.Outer portion 30 defines, in conjunction with bore 31, annular feedpassages 35 and 36 which are connected respectfully with the accumulator10c and the actuator 12. Two further annular feed passages 51 and 52 arealso defined in a similar manner, feed passage 51 being connected withpump 10b and passage 52 with steering valve 50.

Within outer valve portion 30 is disposed an axially movable landedspool 37 which, when the solenoid valve 12a is not actuated it ismaintained in the position shown in FIG. 1 by return springs 38 and 39respectively. Return spring 39 acts against a threaded nut 40 whoseaxial position within a threaded bore 41 controls the spring loading onspool 37 as described in the Applicants co pending application no.9308539.7.

When the spool 37 is in the FIG. 1 position, spool land 42 cuts offcommunication between annular feed passages 35 and 36 so that thechamber 18 of actuator 12 is not pressurised by the powerpack 10. Inthis spool position feed passage 36 communicates with reservoir 10a viaflow path X and return line 43.

Spool 37 also includes an additional land 53 provided with an axialgroove 54 which extends part way along land 53. With the spool 37 in theFIG. 1 position, annular feed passage 51 is in unrestrictedcommunication with feed passage 52 via path Y over shoulder 55 in bore30a within which spool 37 slides.

The actuation system is completed by a pressure level sensor 56 whichprovides electrical signals to control unit 36 indicative of thepressure level of the fluid in accumulator 10c. Typically if thepressure level in the accumulator falls below 20 bar this is taken as anindication by control unit 36 that charging of the accumulator isnecessary and a pressure level of say 40 bars indicates a fully chargedaccumulator.

The above described actuation system operates as follows.

With the spool 37 in the FIG. 1 position, as previously indicated,actuator 12 is not pressurised by accumulator 10c so that the clutchoperated by the release bearing 14 is engaged. To disengage the clutchthe solenoid 12b of valve 12a is actuated to axially displace spool 37to the right, as viewed in FIG. 1, so that land 42 opens up acommunication between annular feed passages 35 and 36 and closes off thereturn path X to reservoir 10a thus connecting chamber 18 of actuator 12with accumulator 10c so that piston 17 is displaced to the right, asviewed in FIG. 1, thus displacing fluid out of chamber 19 of actuator 12into slave cylinder 11 to operate clutch release bearing 14 to disengagethe clutch.

It will be appreciated that the above axial movement of spool 37 resultsin the previously unrestricted flow path Y now taking place via theaxial groove 54. The groove 54 is sized such that the volume flow rateavailable to steering valve 50 is still maintained at a sufficientlyhigh level to ensure an unaffected operation of valve 50 whilst at thesame time causing a build up of back pressure on the pump side of thevalve 12a which is sufficient to charge the accumulator 10c.

Should pressure sensor 56 indicate that charging of accumulator 10c isnecessary (as a result of the pressure level having fallen below apredetermined charge level--typically 20 bars) when the clutch actuator12 is not being actuated control unit 36 issues a signal to solenoid 12bto displace spool 37 to the right thus bringing groove 54 into the flowpath Y so that charging of the accumulator 10c can take place withoutany effect on the operation of steering valve 50 and without actuatingslave cylinder 11.

Thus the restricted flow to steering valve 50 via groove 54 isintroduced into the steering circuit when spool 37 is moved by controlunit 36 to operate actuator 12 or, if actuator 12 is not underoperation, when pressure level sensor 56 indicates that charging of theaccumulator is necessary.

The present invention thus provides an actuating system in which theoperation of the open centre steering valve 50 is not effected by thecharging of the accumulator.

With the actuating system described above there is nothing to controlthe level to which the accumulator 10c could be charged by pump 10b whenthe steering is being operated. This may result in the accumulator(which is preferably kept at a pressure level of 30-40 bars) beingcharged to pressure levels well above 100 bars as a result of backpressure generating on the pump side of steering valve 50 since pressurelevels well above 100 bars can be generated in the steering circuit whenthe valve 50 is in, for example, the full lock position.

If desired, the above problem of high accumulator charging pressures canbe overcome by the use of a second valve means 60, shown in dotteddetail in FIG. 1, in the line to the accumulator 10c.

Conveniently, as shown in FIG. 2 the second valve means 60 may comprisea charging valve 114 and venting valve 117 arrangement of the formdescribed in the previously referred to co-pending application Ser. No.9420983.0.

The charging valve 114 comprises a spool 120 with a waisted portion 121which controls communication between charging ports 122 and 123depending on the axial position of the spool. One end 124 of spool 120is acted upon by the charging pressure on the accumulator side ofnon-return valve 10d. The other end of spool 120 is formed as rod 125which is operative to unseat a ball valve member 126 of venting valve117 which is normally held against an associating venting seat 127 by aspring 128. A main spool control spring 129 also acts on spool 120 tobias the spool to the right as viewed in FIG. 2.

As will be evident from the above, the accumulator pressure acting onend 124 of spool 120 acts against the combined action of main spoolcontrol spring 129, light spring 128 and the charging pressure acting onventing valve member 126. The effective cross sectional areas of the end124 of spool 120 and the area of valve member 126 exposed to thecharging pressure are arranged to be substantially different (typicallytwo to one in favour of the end 124 of the spool). Because of the highdifferential areas used, as soon as the accumulator pressure has risensufficiently to open venting valve 117 the pressure surrounding ballvalve member 126 drops dramatically so that the force acting to theright on spool 120 also drops dramatically and the accumulator pressureacting on the end 124 of spool 120 ensures a rapid movement of the spoolto the left to close off charging port 123. This provides a large forceholding venting valve member 126 open so that the pressure on the pumpside of non return valve 10d is vented to the sump 10a via a line 30.This ensures a clear cut-off level at which the charging of accumulator10c is cut-off by spool 120.

Similarly it is necessary for the accumulator pressure to fall to arelatively low level compared with the level at which charging of theaccumulator is cut-off by spool 120 before spring 129 displaces spool120 to open charging port 123 and recommence charging of the accumulator10c. Thus the cut-off of charging and commencement of charging areclearly and efficiently controlled by charging valve 114 and ventingvalve 117 to provide clear and distinct cut-off and recharging pressurelevels.

The clutch actuation system of FIG. 3 is basically the same as that ofFIG. 1 with the exception that in FIG. 3 the accumulator 10c is chargedvia annular feed passages 51 and 52 (see path Y') and power steeringvalve 50 is fed for convenience via charging valve 80 via permanentlyopen feed passage 51. Components of FIG. 3 similar to those of FIG. 2have been similarly numbered.

When the spool 37 is in the FIG. 3 position, spool land 42 cuts offcommunication between annular feed passages 35 and 36 so that thechamber 18 of actuator 12 is not pressurised by the powerpack 10. Inthis spool position feed passage 36 communicates with reservoir 10a viaflow path X and return line 43. and annular feed passage 51 is inunrestricted communication with feed passage 52 via path Y' so that thecharging rate of accumulator 10c is not restricted.

Pressure level sensor 56 provides electrical signals to actuate, viacontrol unit 36, charging valve 80 with a parallel coupled flowrestrictor 81.

Typically if the pressure level in the accumulator falls below 20 barsensor 56 closes charging valve 80 to divert flow to the steering valve50 via flow restriction 81. This causes a back pressure to build up onthe pump side of valve 80 which ensures adequate charging of accumulator10c whilst still ensuring effective operation of steering valve 50.

The actuation system also includes a pressure sensor 90 which producesan output signal to control unit 36 when the pressure in the steeringvalve circuit has risen to 2 to 3 bar thus indicating that the steeringvalve 50 is operative. Operating pressures of 80-100 bar are notuncommon in such steering valve circuits when the valve is in thefull-lock condition.

The actuation system of FIG. 3 operates as follows.

With the spool 37 in the FIG. 3 position, as previously indicated,actuator 12 is not pressurised by accumulator 10c so that the clutchoperated by the release bearing 14 is engaged. To disengage the clutchthe solenoid 12b of valve 12a is actuated to axially displace spool 37to the right, as viewed in FIG. 3, so that the land 42 opens up acommunication between annular feed passages 35 and 36 and closes off thereturn path X to reservoir 10a thus connecting chamber 18 of actuator 12with accumulator 10c so that piston 17 is displaced to the right asviewed in FIG. 3, thus displacing fluid out of chamber 19 of actuator 12into slave cylinder 11 to operate clutch release bearing 14 to disengagethe clutch.

It will be appreciated that the above axial movement of spool 37 resultsin the previously unrestricted accumulator charging path Y' now takingplace via the axial groove 54 in land 53. The groove 54 is sized suchthat the volume flow rate available to charge accumulator 10c ensuresthat sufficient flow is still available to steering valve 50 to ensureunaffected operation of valve 50.

Should pressure sensor 56 indicate that charging of accumulator 10c isnecessary (as a result of the pressure level having fallen below apredetermined charge level--typically 20 bar) control unit 36 issues asignal to charging valve 80 to switch flow through the restrictor 81 tobuild up a back pressure to ensure charging of the accumulator 10c cantake place at a rate which will not effect the operation of steeringvalve 50.

When sensor 90 sends a signal to control unit 36 indicating operation ofsteering valve 50, control unit 36 issues a signal to the solenoid 12bof valve 12a to move spool 37 to the right sufficient to restricting thecharging flow to accumulator 10c using groove 54 without actuating slavecylinder 11. Thus uneffected operation of steering valve 50 can takeplace during charging of accumulator 10c. With a more sophisticatedcontrol unit 36 the spool 37 may not necessary be displaced on everyoccasion when the steering valve 50 is operating. For example, if thesteering valve is making small steering connection either side of thestraight ahead position, the control unit could be set up to permitunrestricted charging of the accumulator.

Again as described in relation to FIG. 1, if desired, the problem ofhigh accumulator charging pressures can be overcome by the use of asecond valve means 60, shown in dotted detail in FIG. 3, in the line tothe accumulator 10c.

Conveniently, the second valve means 60 may comprise a charging valve114 and venting valve 117 arrangement similar to that described inrelation to FIG. 2.

Referring to FIG. 4 this shows an actuation system employing such acharging valve 114 and venting valve 117 arrangement the charging valve114 comprising a spool 120 with two waisted portions 121a and 121b ascompared with the single waisted portion 121 in FIG. 2. Waisted portion121a controls communications between charging ports 122 and 123depending on the axial position of the spool. Waisted portion 121b andan associated axially extending flow restricting groove 181a controlflow through a steering port 181 which performs the function ofresrictor 81 in the FIG. 3 construction.

One end 124 of spool 120 is acted upon by the charging pressure on theaccumulator side of non-return valve 10d. The rod end 125 of spool 120is operative to unseat ball valve member 126 of venting valve 117 whichis normally held against an associating venting seat 127 by a spring128. A main spool control spring 129 also acts on spool 120 to bias thespool to the left as viewed in FIG. 4.

As will be evident from the above, the accumulator pressure acting onend 124 of spool 120 acts against the combined action of main spoolcontrol spring 129, light spring 128 and the charging pressure acting onventing valve member 126. The effective cross sectional areas of the end124 of spool 120 and the area of valve member 126 exposed to thecharging pressure are arranged to be substantially different (typicallytwo to one in favour of the end 124 of the spool). Because of the highdifferential areas used, as soon as the accumulator pressure has risensufficiently to open venting valve 117 the pressure surrounding ballvalve member 126 drops dramatically so that the force acting to the lefton spool 120 also drop dramatically and the accumulator pressure actingon the end 124 of spool 120 ensures a rapid movement of the spool to theright to close off charging port 123. This provides a large forceholding venting valve member 126 open so that the pressure on the pumpside of non return valve 10d is vented to the sump 10a via a line 30.This ensures a clear cut-off level at which the charging of accumulator10c is cut-off by spool 120.

Similarly it is necessary for the accumulator pressure to fall to arelatively low level compared with the level at which charging of theaccumulator is cut off by spool 120 before spring 129 displaces spool120 to open charging port 123 and recommence charging of the accumulator10c. Thus the cut-off of charging and commencement of charging areclearly and efficiently controlled by charging valve 114 and ventingvalve 117 to provide clear and distinct cut-off and recharging pressurelevels.

As will be apparent from the above, flow restricting groove 181aco-operates with steering port 181 to restrict the flow of fluid tosteering valve 50 when charging port 123 is open and accumulator 10c isbeing charged by pump 10b. This restriction of the steering circuit isremoved when spool 120 is moved to the right to close off port 123.

Thus in the FIG. 4 construction the extra waisted portion 121b, on spool120 with its co-operating steering port 181 and groove 181a replace thefunction of charging valve 80, restrictor 81 and pressure sensor 56 inthe FIG. 3 construction.

FIG. 5 shows part of a modified form of the system shown in FIG. 4 inwhich pressure sensor 90 which operates the solenoid valve 12a isreplaced by a pressure tapping 200 from the steering circuit betweensteering valve 50 and charging/venting valve 114/117. Tapping 200 isconnected with an auxiliary piston 201 which acts on the end of thespool 37 of valve 12a to displace spool 37 when the pressure level intapping 200 indicates that the steering valve 50 is being operated thusrestricting the potential charging rate of accumulator 10c.

The solenoid actuation of spool 37 to control the pressure supplied toactuator 12 is still retained down the centre of piston 201 as indicateddiagrammatically at 12b in FIG. 5.

I claim:
 1. An actuation system comprising:at least one first consumeractuated from the pump; at least one second consumer actuated via avalve means from an accumulator charged by the pump; the valve meansbeing operable to connect said at least one second consumer to theaccumulator or to the reservoir thus actuating said at least one secondconsumer and also being operable in response to accumulator pressurelevels below a predetermined charge level to restrict the flow of fluidto said at least one first consumer to a level sufficient to ensureeffective operation of said at least one first consumer while generatinga back pressure sufficient to ensure charging of the accumulator; thevalve means including a valve having a valve member which isdisplaceable both to connect said at least one second consumer to theaccumulator or reservoir and also to restrict the flow of fluid to saidat least one consumer.
 2. A system according to claim 1 in which boththe first and second consumers are actuated via the valve means.
 3. Asystem according to claim 2 which includes second valve means whichlimits the pressure level to which the accumulator can be charged.
 4. Asystem according to claim 1 in which the valve member is displaced by asolenoid which is activated both by a control means and also by signalsfrom an accumulator pressure level sensor.
 5. A system according toclaim 1 in which the valve member is displaced by a solenoid which isactivated both by a control means and also by a direct action ofaccumulator pressure on the valve member.
 6. A system according to claim1 in which the valve member is a spool having groove means through whichthe restricted communication to said at least one first consumer takesplace.
 7. A system according to claim 1 which includes second valvemeans which limits the pressure level to which the accumulator can becharged.
 8. An actuation system comprising:at least one first consumeractuated from the pump; at least one second consumer actuated via avalve means from an accumulator charged by the pump; the valve meansbeing operable to connect said at least one second consumer to theaccumulator or to the reservoir thus actuating said at least one secondconsumer and also being operable in response to accumulator pressurelevels below a predetermined charge level to restrict the flow of fluidto said at least one first consumer to a level sufficient to ensureeffective operation of said at least one first consumer while generatinga back pressure sufficient to ensure charging of the accumulator; thevalve means includes a valve having a valve member which is displacedboth to connect said least one second consumer to the accumulator orreservoir and also to control a rate of charging of the accumulator. 9.A system according to claim 8 in which the valve member is displaced bya solenoid which is activated both by a control means and also bysignals indicating operation of said at least one first consumer.
 10. Asystem according to claim 9 in which the operation of said at least onefirst consumer is detected by a pressure level sensor which indicates arise in pressure indicative of the operation of said at least one firstconsumer.
 11. A system according to claim to claim 9 in which theoperation of said at least one first consumer is detected by a pressuretapping from said at least one first consumer which directs pressureonto the valve member.
 12. A system according to claim 9 in which thevalve means also includes a separate charging valve means to restrictthe flow of fluid to said at least one first consumer at accumulatorpressure levels below said predetermined charge level.
 13. A systemaccording to claim 9 in which the valve member is a spool having groovemeans through which the restricted communication for the accumulatortakes place.
 14. A system according to claim 8 in which the valve meansalso includes a separate charging valve means to restrict the flow offluid to said at least one first consumer at accumulator pressure levelsbelow said predetermined charge level.
 15. A system according to claim14 in which the charging valve means comprises a solenoid operated valvewhich switches flow to said at least one first consumer through a flowrestrictor at accumulator pressure levels below said predeterminedcharge level.
 16. A system according to claim 8 in which the valvemember is a spool having groove means through which the restrictedcommunication for the accumulator takes place.